Hitherto, in a seat belt apparatus for use in a motor vehicle, or the like, a buckle apparatus for fixing an end portion of webbing (belt) that keeps an occupant under restraint, or the buckle apparatus for fixing a tongue being provided at a turned back end portion of the webbing to a motor vehicle is provided.
FIGS. 8(a), 8(b), and 9 illustrate an example of such a buckle apparatus in a conventional technology, in which FIG. 8(a) is a longitudinal cross-section illustrating a buckle apparatus where a tongue is in a non-latched (disengaged) state with the buckle apparatus, FIG. 8(b) is a longitudinal cross-section illustrating the buckle apparatus where the tongue is in a latched (engaged) state with the buckle apparatus, and FIG. 9 is an exploded perspective view illustrating an entire structure of the buckle apparatus. In addition, part of constituting elements shown in FIG. 9 is omitted in FIGS. 8(a) and 8(b) to avoid complication of the drawings.
 (1) Entire Construction of the Buckle Apparatus
In FIGS. 8(a), 8(b), and 9, a buckle apparatus 1 is having following elements, i.e., a base 2 formed of a U-shaped frame having two of a left and a right side walls, 2a and 2b, and a bottom portion 2c, a latch member 4 being rotatably supported by means of both of the side walls, 2a and 2b, of the base 2, and capable of being latched (engaged) with a tongue 3 that serves as a member for a belt, which is to be latched, a slider (locking member) 5 that is movably supported by means of the latch member 4 for relative movement on an upper face of the latch member 4, and that prevents the latch member 4 from moving in a releasing direction for a latched state of the latch member 4 when the tongue 3 and the latch member 4 are latched with each other, a slider spring 6 that always causes the slider 5 to be biased toward the latch member 4 by means of being compressed between the slider 5 and the latch member 4, a locking pin 7 being rotatably supported by means of holes, 2d and 2e, of both of the side walls, 2a and 2b, of the base 2, which presses (locks) an upper face of the slider 5 that prevents the latch member 4 from moving in the releasing direction for the latched state of the latch member 4 when the tongue 3 and the latch member 4 are latched with each other, a release button (operation member) 8 movably provided in a longitudinal direction at both of the side walls, 2a and 2b, of the base 2, an inertia lever 9 positioned between a release button 8 and the latch member 4 and being rotatably supported by means of grooves, 2f and 2g, of both of the side walls, 2a and 2b, an ejector 10 being slidably provided in a longitudinal direction of the base 2 at a bottom portion 2c of the base 2 and separating the tongue 3 from the buckle apparatus 1, an ejector spring 11 that always keeps the ejector 10 being biased in a direction for the tongue 3 to be separated from the buckle apparatus 1, and covers (an upper cover UC and a lower cover LC) that include these elements described above in a manner so as to cover from above and below.
The latch member 4 is provided with rotating shafts, 4a and 4b and the rotating shafts, 4a and 4b, are rotatably supported by means of supporting grooves, 2h and 2i, formed in both of the side walls, 2a and 2b, of the base 2. In this case, the latch member 4 is biased in a clockwise direction in the drawings by means of the slider spring 6, in the disengaged (non-latched) state shown in FIG. 8(a), and the latch member 4 is biased also in the clockwise direction in the drawings by means of the ejector spring 11 in the latched state, shown in FIG. 8(b). As a result, the latch member 4 is always biased by means of either one of two springs, 6 and 11. Further, the latch member 4 is provided with a pair of arms, 4d and 4e, which is extended from the rotation shafts, 4a and 4b, each of tip end portions of which serves as portions, 4d1 and 4e1, to be pressed. Both of these portions, 4d1 and 4e1, to be pressed are respectively constructed to be capable of being pressed rightward in FIG. 8(a) by means of pressing portions, 10a and 10b (shown in FIG. 9), of the ejector 10 at a right end thereof, as described later.
The slider 5 is provided with a protruding shaft 5a at a center thereof extending in a longitudinal direction of the buckle apparatus 1 and the protruding shaft 5a is penetrating through a hole 4c of the latch member 4. In addition, the protruding shaft 5a is fit into the slider spring 6 and the slider spring 6 is compressed by being sandwiched between the latch member 4 and the slider 5. Further, the slider 5 is provided with a pair of left and right engaging shafts, 5b and 5c. 
The pair of the engaging shafts, 5b and 5c are respectively engaged and supported by means of engaging grooves, 2j and 2k, respectively formed at both of the side walls, 2a and 2b of the base 2, and are protruding outward in a predetermined amount from both of the side walls, 2a and 2b. In this case, both of the engaging grooves, 2j and 2k, respectively having first groove portions, 2j1 and 2k1, both of which are extending in a longitudinal direction (namely, the moving direction of the release button 8) of the buckle 1, and second groove portions, 2j2 and 2k2, extending upward in a sloping manner from these first groove portions, 2j1 and 2k1, in an opening manner. Further, the engaging shafts, 5b and 5c of the slider 5 are respectively configured to be movable along the first groove portions, 2j1 and 2k1, in usual operation, and are configured to be movable along the first groove portions, 2j1 and 2k1, and the second groove portions, 2j2 and 2k2, in an unusual operation, i.e., when the latched state is forcibly released.
On the other hand, the side walls, 2a and 2b, of the buckle apparatus 1 including each of the grooves and the holes have line symmetry at a center line in a longitudinal direction of the buckle apparatus 1.
The release button 8 is provided with a left and a right side walls, 8a and 8b, extending in a longitudinal direction of the buckle apparatus 1, and a left and a right protruding portions 8c (although only one protruding portion is shown and the other protruding portion is not shown, both of the protruding portions are denoted by 8c, as a matter of convenience for later explanation.) extending in a longitudinal direction of the buckle apparatus 1 are respectively provided between the side walls, 8a and 8b, as shown in FIG. 9. A pressing portion 8f that is having a vertical face (in a similar manner, both of the pressing portions are hereinafter denoted by 8f.), which presses each of the engaging shafts, 5b and 5c, of the slider 5 so as to move the same in a releasing direction when the releasing button 8 is moved in a releasing direction, is formed in each of the internal faces of both of the side walls, 8a and 8b. 
On the other hand, similar to the side walls, 2a and 2b, of the buckle apparatus 1, both of the side walls, 8a and 8b, of the release button 8 have line symmetry at the center line in a longitudinal direction of the buckle apparatus 1.
The inertia lever 9 is provided with a pair of left and right rotation shafts, 9a and 9b, and these rotation shafts, 9a and 9b, are rotatably fit into the grooves, 2f and 2g, of both of the side walls, 2a and 2b, of the base 2. Further, the inertia lever 9 is provided with a lever-side engaging connecting portion 9c formed of a round pin-like shape having a round cross-section.
 (2) Basic Motion of the Buckle Apparatus
Next, a latching motion of the buckle apparatus 1 with the tongue 3 in the thus constructed present embodiment will be explained.
In the non-latched state of the buckle apparatus 1 where the tongue 3 is not inserted thereto, a position of the ejector 10 is set to that of a leftmost limit by means of spring force of the ejector spring 11, as shown in FIG. 8(a). In the leftmost limit position of the ejector 10, the latch member 4 is rotated in an upper direction (in a clockwise direction from the latched state) in relationship among the slider 5, the locking pin 7, and the slider spring 6. At this moment, the slider 5 is disengaged from the locking pin 7 and is positioned to be upwardly rotated. As a result, an upper face of the latch member 4 is kept in contact with a lower face of the locking pin 7. In this state, a joggle portion 4f of the latch member 4 is moved away from the inserting path of the tongue 3 and the latch member 4 is set to be at a non-latching position where the joggle portion 4f is not latched with the tongue 3.
When the tongue 3 is inserted through an opening (tongue insertion inlet) 1a that is provided at one side end portion (left end portion in the middle in FIGS. 8(a) and 8(b)) of the upper cover UC of the buckle apparatus 1, in the non-latched state of the buckle apparatus 1, a right end of the tongue 3 is caused to be in contact with a left end of the ejector 10 and the ejector 10 is pressed rightward. Then, because the ejector 10 moves rightward compressing the ejector spring 11 corresponding to an inserting amount of the tongue 3, a suppressing portions 10a and 10b of the ejector 10 presses the portions, 4d1 and 4e1, of the latch member 4 to be pressed, in a rightward direction and thereby the latch member 4 is downwardly (in a counterclockwise direction) rotated. Consequently, the joggle portion 4f of the latch member 4 proceeds to a moving path of the tongue 3 and is fit into a latching hole 3a of the tongue 3. Accordingly, the latch member 4 is in a latching position. Further, when inserting force of the tongue 3 is released, the ejector 10 presses the right end of the tongue 3 by means of spring force of the ejector spring 11; a right end portion of the latching hole 3a of the tongue 3 is engaged with the joggle portion 4f; the tongue 3 is latched with the buckle apparatus 1; and the tongue 3 and the buckle apparatus 1 are caused to be in a latched state, shown in FIG. 8(b).
At this moment, the slider 5 proceeds to a position below the locking pin 7 by means of the spring force of the slider spring 6, and an upper face of the slider 5 is pressed by the locking pin 7. Accordingly, the latch member 4 cannot be pulled out from the latching hole 3a of the tongue 3 and the latched state of the tongue 3 and the buckle apparatus 1 are firmly maintained. This is because the slider 5 holds the latch member 4 at a latching position, shown in FIG. 8(b).
When the release button 8 is pressed rightward so as to release the latched state of the tongue 3 and the buckle apparatus 1, shown in FIG. 8(b), the release button 8 is moved rightward. Further, a pressing portion 8f of the release button 8 presses each of the engaging shafts, 5b and 5c, of the slider 5 rightward, and the slider 5 is moved rightward, i.e., in a direction toward the latch member 4, against the biasing force of the slider spring 6. Then, the engaging shafts, 5b and 5c, of the slider 5 are displaced from the first groove portions, 2j1 and 2k1, and a left end upper face of the slider 5 is displaced from a lower face of the locking pin 7. As a result, the slider 5 is caused not to be pressed by means of the locking pin 7.
Then, the slider 5 and the latch member 4 are rotated in a clockwise direction and the joggle portion 4f is moved upward. The ejector 10 strikes up the latch member 4 via the tongue 3; the latch member 4 and the slider 5 are further rotated in a clockwise direction around the rotation shafts, 4a and 4b, as a rotation center; the joggle portion 4f is displaced away from the latching hole 3a of the tongue 3; and at the same time, the tongue 3 is pushed out in a left direction. This is because the ejector 10 is biased in a direction for releasing the latched state by the spring force of the ejector spring 11.
As shown in FIG. 8(a), when an upper face of a joggle portion 4f side of the latch member 4 is caused to be in contact with the locking pin 7, the rotation of the latch member 4 and the slider 5 in a clockwise direction is stopped. At this moment, a left end of the slider 5 is caused to be in contact with the locking pin 7 by means of the tension force of the slider spring 6. Finally, the ejector 10 is located at a leftmost limit position, and the latch member 4 is located at a non-latching position. Consequently, the buckle apparatus 1 is in the non-latched state where the tongue 3 is displaced.
In addition, for switching the aforementioned positions of the buckle apparatus 1 and the tongue 3, from the latched position to the non-latched position, and vice versa, a magnet 50 (a permanent magnet) for detecting the latched state is provided in the slider 5, as shown in FIG. 9. Correspondingly, a magnet sensor 100 for generating electromotive force by means of a magnetic field of the aforementioned magnet 50 is provided in a sensor holder 60 whose claw portions, 60a and 60b, are latched with a engaging holes, 2p and 2q, of both of the side walls, 2a and 2b, of the base 2. The magnet sensor 100 detects whether the slider 5 is contiguous to (corresponding to the non-latched state) or distant from (corresponding to the latched state) the magnet sensor 100 on the basis of that the magnet field is small or large, and outputs corresponding current value, for example.
On the other hand, in such a buckle apparatus 1, particularly, at a nighttime or the like, when an inside of a room of the motor vehicle is in a state of a darkroom, a buckle apparatus provided with an illuminating function to ease recognition for a position of the buckle apparatus 1, or to ease recognition for an inserting opening of the buckle apparatus 1 for inserting the tongue 3, is known (for example, refer to Japanese Unexamined Utility Model Registration Application Publication No. 5-53508).
FIG. 7 is a perspective view illustrating a built-in illumination apparatus for the buckle apparatus of the aforementioned conventional technology.
In an illumination apparatus, shown in FIG. 7, a printed circuit board 20 is disposed at the aforementioned lower cover LC. A plurality of conductive wiring portions 21 are formed in the printed circuit board 20. Further, a harness 22 connected to a controller (not shown), an LED 23 for illuminating the vicinity of an insertion inlet for the tongue 3, and a resistor 24 for setting electric current supplied to the LED to a predetermined value are connected to the wiring portion 21, by means of soldering.
The LED 23 is disposed in the vicinity of the insertion inlet for the tongue 3, and for example, a portion around the insertion inlet for the tongue 3 is illuminated by emitting light when the controller detects that an occupant is seated in a seat.
In addition, as the upper face view is shown in FIG. 6(a) and the side face view is shown in FIG. 6(b), a reflector (lens) 25 for diffusing and leading light flux of the illumination emitted from the LED 23 is usually disposed at a front face of the LED 23.
On the other hand, in the thus constructed buckle apparatus 1, because a printed circuit board 20 provided with an LED 23 is disposed at almost all over the lower cover LC, large space is required to be secured. Therefore, space in the upper cover UC and the lower cover LC for the members to be mounted on (mounting space) is limited. In other words, the mounting space in the upper cover UC and the lower cover LC for the members other than that described above, for example, a detection system, such as the aforementioned magnet sensor 100 or the like, a drive system, such as the latch member 4, the slider 5, and the like, and other system is compressed. Consequently, it is likely to decrease flexibility for designing.